Mixed-function oxidases containing different forms of cytochrome P-450 are the critical enzymes that metabolize a wide variety of drugs, chemicals and carcinogens. The focus of this project is the utilization of specific inhibitors and inducers of aryl hydrocarbon hydroxylase (AHH) to probe the multiplicity, diversity and different catalytic properties of the cytochrome P-450s. The form of AHH that is induced by polycyclic hydrocarbons is strongly inhibited by 7, 8-benzoflavone, but this compound weakly inhibits or stimulates the form of AHH from untreated or phenabarbital-treated rats. In contrast, 1-Maackiain acetate greatly inhibits the AHH from untreated or phenobarbital-treated rats, and weakly inhibits or stimulates the form of AHH induced by polycyclic hydrocarbons. Therefore, 7, 8-benzoflavone and 1-Maackiain acetate are inhibitors that are effective against different forms of AHH. We are using these inhibitors to probe the enzymology and active catalytic sites of the multiple forms of the cytochromes P-450.